knocking noise only at idle when the car is 1st started

[Big Dawg1]

My 90' non-turbo has 178,000 miles. The other day I noticed that after I started the car and got out, I heard a faint knocking sound at idle. Not a ticking sound but a sound like hitting your knuckle on a solid piece of wood. After a few minutes the noise goes away as the car gets up to running temps.

Although I bought it new in 1990, it hasn't been my daily driver for years so I only drive it approximately 1,000 miles per year now. I have always maintained the car very well and change the oil every 3,000 miles regardless of what the so called experts recommend.
Other than that noise when the car is first started cold, it runs great.

I realize it could be many things, but does anyone have any suggestions?

BD

[z.Leinbach]

does it sound like a thump thump or tack tack

[Big Dawg1]

not a tapping sound nor a tick tick sound, but like I explained, a deep knocking sound similar to what you would hear if you hit your knuckle on a solid wood door.

[z.Leinbach]

Possibly be piston slap or worn out rods

[Big Dawg1]

Yea I was thinking it could either be the crank shaft bearing or one of the piston rod bearings. Thanks for the info.
If it is the piston rod bearing, does anyone have any idea if it can be repaired while the engine is still in the car on my '90 300ZX?

[z.Leinbach]

Unfortunately any internal work, or even oil pan work the engine should come out, cause pulling cross members arenot easy to get off unless you've done it 3 or 4 times

[nissanfreak12]

When was the last time you changed your oil? What kind of filter do you use? Do you do it yourself or go through a quick lube place?

[Big Dawg1]

nissanfreak12
As I mentioned, I get an oil change every 3,000 miles. I never do it myself.

z.Leinbach
Assuming it is rod bearings, do you have a ball park idea what the cost will be to replace them all?

[RubyRed300ZX]

"Bought it new in 1990 ... only drives it 1,000 miles a year now"

It needs an Italian Tune-up. What you are hearing is carbon build-up on top of one of the pistons or the head.

[z.Leinbach]

37hour job might as well do a full overhaul. Depending on what you dealerlabor cost is probably around 170$/hr. I'd say time to upgrade and it back in the road, they are to timeless to sit.

Italian tune up glad to hear someone else use this reference lollolx.
Compression check, Plugs, coils, pcvs, fuel.filter, fuel pressure check, healthy dose of injector cleaner, engine flush and good oil, then find the high way. An braaaaap

[RubyRed300ZX]

That was a quick reply earlier. I'll elaborate. You bought it new in 1990. I bought mine new in 1993; so, I am assuming we're about the same age. Though the same age, I drive like I'm 22 ... like I just stole it. Mine has never had a chance to build up carbon.

You should buy a bottle of Seafoam engine treatment (not the transmission treatment) which is okay for you to use in that you have an N/A and not the TT. Pour it into the gas tank, fill the gas tank (with non-oxygenated fuel) to mix it thoroughly, and drive for 20 minutes. Then park it for a couple days. Pull it out after that, let it warm up fully (until the knock noise goes away), then take it for a robust drive. Not a highway slog. Head out to the open country where you can have some fun. Row through the gears. Bump up against the rev limiter more than a couple times. Lay down some rubber from a standing stop, and into second gear, and into 3rd gear. Have some fun. When the tank is half empty, head for home and park it. Let it sit for another day. Problem solved for $20 (can of Seafoam and that 1/2 tank of fuel). Plus you should still have a smile on your face. You should look like this for at least a week if you did it right.

[Big Dawg1]

RubyRed300ZX
Thanks for the info.
It may not fix my issue but it will surely be fun trying.

[z.Leinbach]

never doubt the use of a good ol italian tune up, just dont use a drip feed into the plenum cause it will only get half of the plenum